Intermittent Problem

[Laysula]

Today I fitted a new Racor filter and priming bulb connected all the banjo unions with dowty washers. Pumped some fuel from the tank to fill the filter and the bowl filled up with a black viscous liquid. So it looks like the problem is a diesel bug. I have now treated the tank with a shock dose of biocide and I am now constructing a polishing rig to clean the fuel.

 

[mickywillis]

We had a very similar issue to yours on our Yanmar 1GM10 several years ago.
After about 18mths of trying to find the problem, to the point of almost ripping the engine out, I found the problem, purely by accident.
When I changed the secondary fuel filter (the Yanmar one with the paper element filter) one of the metal discs that is fitted to each end of the filter, was still pushed into the top of the filter housing. The metal disc had detatched itself from the end of the filter and stayed in position. When I fitted a new filter, I was able to fit it on top of the stuck metal disc, and re-attach the metal screw on bowl from underneath. There were no leaks from the filter, the engine bled itself OK initially and the engine ran fine. It was only when running under load, that the misfiring, slowing down and then eventually cutting out became apparent. I posted here on the forum and had all sorts of replies, from diesel bug, collapsed fuel lines, poor copper sealing washers, damaged pump diaphragms, etc.

As you say you changed the filters in December and the problem wasnt present before then, it may be worth checking the filter housing and seeing if this may your problem? If I had known this at the time, it would have saved 18 mths of worry and cancelled trips!

 

[B58]

Today I fitted a new Racor filter and priming bulb connected all the banjo unions with dowty washers. Pumped some fuel from the tank to fill the filter and the bowl filled up with a black viscous liquid. So it looks like the problem is a diesel bug. I have now treated the tank with a shock dose of biocide and I am now constructing a polishing rig to clean the fuel.

Polishing may help, but the black viscus fluid could be aspheltines, tank needs to be cleaned including all fuel pipes an fie equipment, what fuel are you using?

 

[Keith-i]

If your tank looks clean, don't rule out the pickup pipe being the culprit. I had a similar porblem of black crud appearing in the filter even thought the tank contents looked fine. It turned out to be the copper pickup tube degrading and being coated in some form of bug residue.

 

[Laysula]

Polishing may help, but the black viscus fluid could be aspheltines, tank needs to be cleaned including all fuel pipes an fie equipment, what fuel are you using?

Cleaning the tank may well be a last resort as there is no inspection hatch and doesn't look the easiest to remove. Fuel has been fame free from MDL for the past 6 years with one top up at Roscoff 3 years ago.

 

[B58]

If Fame free, it must be MDO?

 

[TernVI]

If your tank looks clean, don't rule out the pickup pipe being the culprit. I had a similar porblem of black crud appearing in the filter even thought the tank contents looked fine. It turned out to be the copper pickup tube degrading and being coated in some form of bug residue.

You shouldn't use copper tube with modern fuels.
It tends to catalyse the degradation of the fuel producing black oily/tarry substances including the ashphaltenes.

But diesel bug can also produce a variety of fallout, from great clumps which block pipes to fine sediment or suspended dark colour.
Once some snake oil has been added, the detritus may be broken down and more mixed with the fuel.

 

[Laysula]

If your tank looks clean, don't rule out the pickup pipe being the culprit. I had a similar porblem of black crud appearing in the filter even thought the tank contents looked fine. It turned out to be the copper pickup tube degrading and being coated in some form of bug residue.

You shouldn't use copper tube with modern fuels.
It tends to catalyse the degradation of the fuel producing black oily/tarry substances including the ashphaltenes.

But diesel bug can also produce a variety of fallout, from great clumps which block pipes to fine sediment or suspended dark colour.
Once some snake oil has been added, the detritus may be broken down and more mixed with the fuel.

Tank is stainless steel so I am presuming that the pickup pipes are also stainless

 

[Laysula]

Quick update. Fuel has been polished over several days, a couple of hours at a time and Marine 16 diesel bug killer added. We had a fair bit of black dust pumped into the filter at first but now it is sparkly clean in and out. Engine bled and run under load for half an hour with no problems and the fuel in the filter bowl still clean. Fingers crossed everything is ok now.